We're told the amoxicillin was prescribed recently because Whitney had been suffering from a sore throat.

We're told some of the pills were old ... some issued in 2011 ... but some of the bottles were from 2012. We're told the bottles that were recovered at the scene did not contain a lot of pills.

Sources tell us ... some of the prescriptions were filled at the infamous Mickey Fine pharmacy in Beverly Hills ... where Michael Jackson had numerous prescriptions filled for Demerol and other drugs.

Law enforcement sources tell us ... it's possible Whitney suffered a heart attack caused by an adverse reaction to her medication, but it is simply too early to make an official call on the cause of death.

We're told the L.A. Coroner's Office has removed the hold on Whitney's body ... which means her family can now have Whitney transported back to Atlanta, where the singer will be laid to rest.